Peak detectors are used to detect the peak amplitude of a signal, such as an analog electronic signal. Examples of peak detector units are described in U.S. Pat. No. 6,188,250; U.S. Pat. No. 6,191,621; and U.S. Pat. No. 5,594,384, which are incorporated herein by reference. The main shortcomings of known peak detectors are caused by factors such as capacitor leakage, voltage drop in rectifying diodes, and slow amplifier feedback. An improved peak detector is desirable.